Method and apparatus for receiving signal for mimo system

ABSTRACT

Provided is a method and apparatus for receiving a signal for a MIMO system. The receiving apparatus includes: a QR decomposer for calculating a unitary matrix Q, an upper triangle matrix R, and a vector size for a received signal; a multiple dimension detector for calculating a first LLR for an output of the QR decomposer through multiple dimension detection; an inverse matrix and weight calculator for calculating an inverse matrix for the upper triangle matrix R and a weight; an interference remover for regenerating a symbol for a demodulated data stream using the fist LLR and removing interference from an output vector of the QR decomposer using the regenerated symbol; and a weight zero forcing unit for performing zero forcing on the interference removed output vector from the interference remover using the inverse matrix of the upper triangle matrix R and the weight and calculating a second LLR.

TECHNICAL FIELD

The present invention relates to a method and apparatus for receiving asignal for a multiple input multiple output (MIMO) system; and, moreparticularly, to a method and apparatus for receiving a signal for aMIMO system, which improve reception performance with hardwarecomplexity reduced by re-generating a symbol corresponding to a datastream demodulated by a multidimensional detector and demodulatingremaining signals after removing the re-generated symbols from areceived signal.

This work was supported by the IT R&D program of MIC/IITA[2006-S-002-02, “IMT-Advanced Radio Transmission Technology with lowMobility”].

BACKGROUND ART

It is a requirement of a wireless communication system to transmit alarge amount of high quality multimedia data using a limited frequency.As a method for transmitting a large amount of data using a limitedfrequency, a multiple input and multiple output (MIMO) system wasintroduced. The MIMO system forms a plural of independent fadingchannels using a multiple antenna at receiving and transmitting ends andtransmits different signals through each of transmitting antennas,thereby significantly increasing a data transmission rate. Accordingly,the MIMO system can transmit a large amount of data without expansion ofa frequency.

However, the MIMO system has a shortcoming that the MIMO system is toofragile for inter-symbol interference (ISI) and frequency selectivefading. In order to overcome the shortcoming, an orthogonal frequencydivision multiplexing (OFDM) scheme was used. The OFDM scheme is themost proper modulation scheme for transmitting data at a high speed. TheOFDM scheme transmits one data row through a subcarrier having a lowdata transmission rate.

A channel environment for wireless communication has multiple paths dueto obstacles such as a building. In a wireless channel environmenthaving multi-paths, delay spray is generated due to the multiple paths.If a time of delay spray is longer than a time of transmitting a nextsymbol, inter-symbol interference (ISI) is generated. In this case,fading is selectively generated in a frequency domain (frequencyselective fading). In case of using single carrier, an equalizer is usedto remove the ISI. However, complexity of the equalizer increases if adata transmission rate increases.

The shortcomings of the MIMO system can be attenuated using anorthogonal frequency division multiplexing (OFDM) technology. In orderto overcome the shortcomings of the MIMO system with the advantages ofthe MIMO system maintained, an OFDM technology was applied to a MIMOsystem having N transmitting antennas and N receiving antennas. That is,a MIMO-OFDM system was introduced.

FIGS. 1 and 2 are a block diagram schematically illustrating a multipleinput multiple output (MIMO) orthogonal frequency division multiplexing(OFDM) system. FIG. 1 is a block diagram of a transmitting end in theMIMO-OFDM system, and FIG. 2 is a block diagram of a receiving end inthe MIMO-OFDM system.

Referring to FIG. 1, the transmitting side includes a serial/parallel(S/P) converter, a plurality of encoders 102, a plurality of quadratureamplitude modulation (QAM) mappers 103, a plurality of inverse fastfourier transform (IFFT) units 104, a plurality of cyclic prefix (CP)inserters 105, and digital/analog and radio frequency (D/A & RF)converting units 106. The S/P converter divides transmission data into aplurality of data rows before encoding the transmission data. Theplurality of encoders 102 encode the data rows. After encoding, theplurality of QAM mappers 103 modulate the encoded data rows based on apredetermined modulation scheme such as binary phase shift keying(BPSK), quadrature phase shift keying (QPSK), 16 QAM, and 64 QAM. Theplurality of IFFT units 104 transform the modulated symbols into timedomain signals. The plurality of CP inserters 105 insert a CP code for aguard interval into the time domain signals. Then, the plurality of D/A& RF converting units 106 convert the CP inserted digital signals toanalog signals and covert the analog signals to RF signals. The RFsignals are transmitted through an antenna.

Referring to FIG. 2, the receiving side includes a plurality ofanalog/digital and radio frequency (A/D & RF) converting units 107, aplurality of CP removers 108, a plurality of fast fourier transform(FFT) units 109, a MIMO receiver, a plurality of decoders 111, and a P/Sconverter 112. The plurality of A/D & RF converting units 107 convert RFsignals to analog signals and convert the analog signals to digitalsignals. The plurality of CP removers 108 remove CP codes which wereinserted for a guard interval and transfer the CP code removed signalsto the FFT units 109. The plurality of FFT units 109 perform FFT on theinput parallel signals which are the CP removed signals. The MIMOreceiver 110 estimate transmission data symbols which are generated byFFT. The MIMO receiver 110 calculates a log likelihood ratio (LLR) fromthe estimated symbols. The plurality of decoders 111 decode each of datarows transferred from the MIMO receiver 110 and estimate thetransmission data. The plurality of P/S converters 112 convert paralleldata modulated by each decoder 111 to serial data.

The MIMO receiver 110 generally uses a decision feedback equalizer(DFE), zero forcing (ZF), minimum mean square error estimation (MMSE),and bell labs layered space-time (BLAST). As described above, the MIMOreceiver has a problem of low performance although the MIMO receiver hasa comparative simple structure compared to maximum likelihood detection(MLD).

DISCLOSURE OF INVENTION Technical Problem

An embodiment of the present invention is directed to providing a methodand apparatus for receiving a signal for a MIMO system, which improvereception performance with hardware complexity reduced by re-generatinga symbol corresponding to a data stream demodulated by amultidimensional detector and demodulating remaining signals afterremoving the re-generated symbols from a received signal.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art of the present invention that the objects andadvantages of the present invention can be realized by the means asclaimed and combinations thereof.

Technical Solution

In accordance with an aspect of the present invention, there is provideda receiving apparatus of an orthogonal frequency division multiplexing(OFDM) based multiple input multiple output (MIMO) system, including: aQR decomposer for calculating an unitary matrix Q, an upper trianglematrix R, and a vector size for a received signal; a multiple dimensiondetector for calculating a first log likelihood ratio (LLR) for anoutput of the QR decomposer through multiple dimension detection; aninverse matrix and weight calculator for calculating an inverse matrixfor the upper triangle matrix R and a weight; an interference removerfor regenerating a symbol for a demodulated data stream using the fistLLR and removing interference from an output vector of the QR decomposerusing the regenerated symbol; and a weight zero forcing unit forperforming zero forcing on the interference removed output vector fromthe interference remover using the inverse matrix of the upper trianglematrix R and the weight and calculating a second LLR.

The receiving apparatus may further include a signal field detector forreceiving an output vector of the QR decomposer and detecting a signalfield from the output vector.

The receiving apparatus may further include a first decoder forperforming demodulation using the first LLR outputted and the multipledimension detector, and a second decoder for performing demodulationusing the second LLR outputted from the weight zero forcing unit.

In accordance with another aspect of the present invention, there isprovide a receiving method of an OFDM based MIMO system, including:performing QR decomposing for calculating an unitary matrix Q, an uppertriangle matrix R, and a vector size for a received signal; calculatinga first LLR by performing multiple dimension detection on the result ofsaid the QR decomposing; calculating an inverse matrix for the uppertriangle matrix R and calculating a weight; regenerating a symbol for ademodulated data stream using the fist LLR and removing interferencefrom the result of the QR decomposing using the regenerated symbol; andperforming zero forcing on the interference removed output vector usingthe inverse matrix of the upper triangle matrix R and the weight andcalculating a second LLR.

The receiving method may further include: detecting a signal field fromthe result of the QR decomposing.

In accordance with still another embodiment of the present invention,there is provided a receiving apparatus of an OFDM based MIMO system,including: a QR decomposing unit for decomposing an unitary matrix Q andan upper triangle matrix R from a received signal; a multiple dimensiondetecting unit for deciding a m^(th) symbol and a (m-1)^(th) symbolthrough performing multiple dimension detection on an output of the QRdecomposing unit; an interference removing unit for regenerating asymbol corresponding to a demodulated data stream using an output of themultiple dimension detecting unit and removing interference from theoutput of the QR decomposing using the regenerated symbol; and a weightzero forcing unit for performing zero forcing on the interferenceremoved output vector using an inverse matrix of an upper trianglematrix R and a weight.

In accordance with further another embodiment of the present invention,there is provided a receiving method of an OFDM based MIMO system,including: decomposing an unitary matrix Q and an upper triangle matrixR from a received signal; deciding a m^(th) symbol and a (m-1)^(to)symbol through performing multiple dimension detection on an output ofsaid decomposing; regenerating a symbol corresponding to a demodulateddata stream using the output of said deciding and removing interferencefrom the output of said QR decomposing using the regenerated symbol; andperforming zero forcing on the interference removed output vector usingan inverse matrix of an upper triangle matrix R and a weight.

Advantageous Effects

A receiving method and apparatus for a multiple input multiple output(MIMO) system according to an embodiment of the present inventionperform a QR operation on a received signal, calculate a log likelihoodratio (LLR) through multiple dimension detection, regenerate a symbolcorresponding to a demodulated data stream using the LLR, removeinterference from the output vector of the QR operation using theregenerated symbol, performing zero forcing using a weight for theinterference removed output vector and the inverse matrix, the result ofzero forcing is demodulated. Therefore, reception performance can beimproved with hardware complexity reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are block diagrams schematically illustrating a multipleinput multiple output (MIMO) orthogonal frequency division multiplexing(OFDM) system.

FIG. 3 is a diagram schematically illustrating a transmitting ending ofa MIMO-OFDM system where the present invention is applied.

FIG. 4 is a diagram schematically illustrating a receiving ending of aMIMO-OFDM system where the present invention is applied.

FIG. 5 is a diagram illustrating a structure of a transmission frame.

FIG. 6 is a diagram illustrating the MIMO receiving and decoding unit ofFIG. 3 in accordance with an embodiment of the present invention.

FIG. 7 is a diagram for describing operating timing in a transmissionframe structure.

FIG. 8 is a state diagram of a MIMO receiver in accordance with anembodiment of the present invention.

FIG. 9 is a timing diagram illustrating operation timings of a receiverin accordance with an embodiment of the present invention.

FIG. 10 is a block diagram illustrating a QR decomposer in accordancewith an embodiment of the present invention.

FIG. 11 is a block diagram illustrating a multiple dimension detector(MDD) in accordance with an embodiment of the present invention.

FIG. 12 is a block diagram illustrating an 8^(th) symbol detector inaccordance with an embodiment of the present invention.

FIGS. 13 and 14 are diagrams for describing a symbol structure having alattice point.

FIG. 15 is a diagram for describing operations of an inverse matrix andweight calculator and a WZF unit in accordance with an embodiment of thepresent invention.

FIG. 16 is a flowchart illustrating a method for receiving a signal fora MIMO system in accordance with an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The advantages, features and aspects of the invention will becomeapparent from the following description of the embodiments withreference to the accompanying drawings, which is set forth hereinafter.Therefore, those skilled in the field of this art of the presentinvention can embody the technological concept and scope of theinvention easily. In addition, if it is considered that detaileddescription on a related art may obscure the points of the presentinvention, the detailed description will not be provided herein. Thepreferred embodiments of the present invention will be described indetail hereinafter with reference to the attached drawings.

FIG. 3 is a block diagram schematically illustrating a transmitting endof a multiple input multiple output (MIMO) orthogonal frequency divisionmultiplexing (OFDM) system where the present invention is applied.

Referring to FIG. 3, the transmitting side includes a serial/parallel(S/P) converter, g encoders 201, q quadrature amplitude modulation (QAM)mappers 202, a plurality of inverse fast fourier transform (IFFT) units203, a plurality of cyclic prefix (CP) inserters 204, and digital/analogand radio frequency (D/A & RF) converting units 205, where g and q areinteger numbers. The S/P converter receives divides transmission datainto a plurality of data rows. The plurality of data rows are input tothe g encoders 201. The g encoders 201 are connected to the q QAMmappers 202. Each of the QAM mappers 202 may have distinct channel coderates and modulation schemes.

Each of the QAM mappers 202 are sequentially connected to the IFFT units203, the CP inserters 204, and the D/A & RF units 205. Since theoperations of the IFFT units 203, the CP inserters 204, and the D/A & RFunits 205 are identical to those shown in FIG. 1 a, detaileddescriptions thereof are omitted.

FIG. 4 is a diagram schematically illustrating a receiving ending of aMIMO-OFDM system where the present invention is applied.

Referring to FIG. 4, the receiving side includes a plurality ofanalog/digital and radio frequency (A/D & RF) converting units 301, aplurality of CP removers 302, a plurality of fast fourier transform(FFT) units 303, a MIMO receiving and decoding unit 304, and a P/Sconverter. The AID & RF converting unit 301 covert RF signals to analogsignals and convert the analog signals to digital signals. The CPremovers 302 remove CP codes for a guard interval from the digitalsignals. The FFT units 303 perform FFT on the CP code removed signals.

The MIMO receiving and decoding unit 304 is a multidimensional receiverand decoder that demodulates fast-fourier transformed symbols.

In the MIMO system, the number N of antennas for receiving a signal islarger than or equal to the number M of antennas for transmitting asignal. After FFT, a received vector Z at a subcarrier can be expressedas Equation 1.

z=Hs+n  Eq. 1

In Equation 1, the vector Z is

${Z = \begin{bmatrix}Z_{1} \\Z_{2} \\\vdots \\Z_{N}\end{bmatrix}},$

a channel H is

${H = \begin{bmatrix}h_{1,1} & h_{1,2} & \cdots & h_{1,M} \\h_{2,1} & h_{2,2} & \cdots & h_{2,M} \\\vdots & \vdots & \ddots & \vdots \\h_{N,1} & h_{N,2} & \cdots & h_{N,M}\end{bmatrix}},$

and a transmitted symbol S is

$S = {\begin{bmatrix}S_{1} \\S_{2} \\\vdots \\S_{M}\end{bmatrix}.}$

After performing the QR operation, the received signal can be expressedas Equation 2.

$\begin{matrix}\begin{matrix}{y = \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{N}\end{bmatrix}} \\{= {Q^{H}z}} \\{= {{Rs} + n^{\prime}}} \\{= {{\begin{bmatrix}r_{1,1} & r_{1,2} & \cdots & r_{1,M} \\0 & r_{2,2} & \cdots & r_{2,M} \\0 & \vdots & \ddots & \vdots \\0 & \cdots & 0 & r_{N,M}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{M}\end{bmatrix}} + \begin{bmatrix}n_{1}^{\prime} \\n_{2}^{\prime} \\\vdots \\n_{N}^{\prime}\end{bmatrix}}}\end{matrix} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

Equation 2 can be simplified into a below equation.

$\begin{matrix}{y = \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{M}\end{bmatrix}} \\{= {Q^{H}z}} \\{= {{Rs} + n^{\prime}}} \\{= {{\begin{bmatrix}r_{1,1} & r_{1,2} & \cdots & r_{1,M} \\0 & r_{2,2} & \cdots & r_{2,M} \\0 & \vdots & \ddots & \vdots \\0 & \cdots & 0 & r_{M,M}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{M}\end{bmatrix}} + \begin{bmatrix}n_{1}^{\prime} \\n_{2}^{\prime} \\\vdots \\n_{N}^{\prime}\end{bmatrix}}}\end{matrix}$

Here, Q is a unitary matrix (Q^(H)Q=I), and R denotes an uppertriangular matrix Since the channel matrix H is N×M, the matrix Q is N×Mand the matrix R is N×M. The matrix Q can be expressed as follow.

$Q = \begin{bmatrix}q_{1,1} & q_{1,2} & q_{1,3} & q_{1,4} & \cdots & q_{1,N} \\q_{2,1} & q_{2,2} & q_{2,3} & q_{2,4} & \cdots & q_{2,N} \\q_{3,1} & q_{3,2} & q_{3,3} & q_{3,4} & \cdots & q_{3,N} \\q_{4,1} & q_{4,2} & q_{4,3} & q_{4,4} & \cdots & q_{4,N} \\\vdots & \vdots & \vdots & \vdots & \ddots & \vdots \\q_{N,1} & q_{N,2} & q_{N,3} & q_{N,4} & \cdots & q_{N,N}\end{bmatrix}$

And, the matrix R can be expressed as follow.

$R = \begin{bmatrix}r_{1,1} & r_{1,2} & \cdots & r_{1,M} \\0 & r_{2,2} & \cdots & r_{2,M} \\\vdots & \vdots & \ddots & \vdots \\0 & 0 & \cdots & r_{M,M} \\0 & 0 & \cdots & 0 \\\vdots & \vdots & \ddots & \vdots \\0 & 0 & \cdots & 0_{N,M}\end{bmatrix}$

FIG. 5 is a diagram illustrating a structure of a transmission frame. Ingeneral, the transmission frame includes 8 symbols of a long trainingfield (LTF) for estimating a channel, a signal field (SIG) for storingframe information, and a plurality of data symbols. In the presentembodiment, the transmission frame is described with M=8 and N=8 forconvenience.

FIG. 6 is a diagram illustrating the MIMO receiving and decoding unit ofFIG. 4 in accordance with an embodiment of the present invention.

Referring to FIG. 6, the MIMO receiving and decoding unit includes a QRdecomposer 501, a multi dimension detector (MDD) 504, a inverse matrixand weight calculator 503, an interference remover 506, a weight zeroforcing (WZF) unit 507, and a plurality of memories.

The QR decomposer 501 calculates a unitary matrix Q, an upper trianglematrix R, and a vector size through QR operation from a received signalZ for a LTF period. The QR decomposer 501 stores the calculated unitarymatrix Q values, upper triangle matrix R values, vector sizes (1√{squareroot over (norm_(i))}) of each element of the unitary matrix Q in thememories 509 to 011. Here, norm is equal to ∥q_(i)∥². The operations ofthe QR decomposer 501 will be described in more detail with reference toFIG. 10 in later.

The signal field detector 502 detects a signal field from an outputvector of the QR decomposers at the SIG period. The inverse matrix andweight calculator 503 reads the upper triangle matrix R values from theR memory 510, reads the vector size (1/√{square root over (norm)}) fromthe vector size memory 511, calculates a inverse matrix of the matrix Rat the first two symbol periods among data symbols, and calculates aweight for zero forcing. The inverse matrix and weight calculator 503stores the calculated inverse matrix of the matrix R and the calculatedweight in the inverse matrix memory 512 and the W memory 513,respectively.

The multiple dimension detector MDD 504 calculates a log likelihoodratio (LLR) through multiple dimensional detection using the outputvector y of the QR decomposer 501 and the upper triangle matrix valuesof the R memory 510. The operations of the MMD 504 will be describedwith reference to FIG. 10 in later. The log likelihood ratio (LLR)value, the output of the MDD 504, is input to the channel decoder 505.The channel decoder 505 performs demodulation using the LLR value.

The interference remover 506 receives values of the Y memory and thevalues of the R memory 510, receives the demodulated data stream fromthe channel decoder 505, generates a symbol corresponding to thedemodulated data stream through symbol mapping, and removes interferencefrom the output vector of the Y memory 514 using the generated symbol.The operations of the interference remover 506 and the inverse matrixand weight calculator 503 will be described with reference to FIG. 13 inlater.

The WZF unit 507 receives the interference removed output vector fromthe interference remover 506, the inverse matrix value of the matrix Rfrom the inverse matrix memory 512, and the weight of the W memory 512.Then, the WZF unit 507 performs zero forcing based on the receivedoutput vector, inverse matrix value, and the weight. The log likelihoodration (LLR) value outputted from the WZF unit 507 is input to thechannel decoder 508.

FIG. 7 is a diagram for describing timing for each operation in atransmission frame structure. Referring to FIG. 6, dtctsycnt denotes asymbol count, and dtctscnt is a sample count increasing according tosample in a symbol. In the present embodiment, one symbol is constructedof 288 samples.

FIG. 8 is a state diagram of a MIMO receiver in accordance with anembodiment of the present invention.

In FIG. 8, RXEN denotes an enable signal for operating a receiver, anddtct_en denotes an enable signal for inputting a received signal z to aMIMO receiver.

Referring to FIG. 8, if a RXEN enable signal and a received signal z areinput when the receiver is in an idle state (IDLE), the state transitsto a LNG state for detecting a long training field (LTF). It transmitsto a SIG state for detecting a signal field if the dtct_en signal isinput and dtctsycnt is 9. After the detection of signal field ends, ittransits to a data modulation state.

FIG. 9 is a timing diagram illustrating operation timings of a receiver.For convenience, FIG. 9 shows the timing diagram when the number of datasymbols is two.

Referring to FIG. 9, fft_o denotes a received signal inputted to a MIMOreceiver. dtctrcnt is a sample counter which is dtctscnt+1. qr_ene is anenable signal for operating a QR decomposer. mrc_ene is an enable signalfor operating the signal field detector 502. And, ir_ene is an enablesignal for calculating a inverse matrix of the matrix R by the inversematrix and weight calculator 503, mdd_ene is an enable signal foroperating the multiple dimension detector 504, and wzf_ene is an enablesignal for performing zero forcing. mdd_ov is an enable signal fortransferring output values of the multiple dimension detector to thechannel decoder 505, wzf_ov is an enable signal for transferring theoutput value of the WZF unit to a decoder, and mdeco_en is an enablesignal for transferring the output value of the channel decoder 505.zdeco_en is an enable signal for transferring the output value of thedecoder 508 to an upper layer.

FIG. 10 is a block diagram illustrating a QR decomposer in accordancewith an embodiment of the present invention.

Referring to FIG. 10, the QR decomposer includes a R calculator 901, a Qupdate calculator 902, a vector size calculator 903, and a Q calculator904. The R calculator 901 calculates each element of an upper trianglematrix R from a received signal Z that is an input signal of a MIMOreceiver. The R calculator 901 stores the calculated matrix R in the Rmemory 510. The R calculator provides the calculated matrix R to thesignal field detector 502 when the mrc_ene signal is on. The Rcalculator stores the calculated matrix R in the Y memory 514 andprovides the calculated matrix R in the MDD 514 at the same time whenthe mdd_ene signal is on.

The Q update calculator 902 calculates a Q update matrix for a receivedsignal Z using elements of the calculated matrix R from the R calculator901. The vector size calculator 903 calculates a norm of a column vectorfrom the calculated Q update matrix and calculates vector sizes √{squareroot over (norm)} and 1/√{square root over (norm)} from a ROM table.Among the vector sizes calculated by the vector size calculator 903, thevector size (1/√{square root over (norm)}) is stored in the vector sizememory 511.

The Q calculator 904 calculates elements of a unitary matrix Q using thecalculated Q update matrix from the Q update calculator 902 and thecalculated vector size from the vector size calculator 903, and storesthe calculated matrix Q into the Q memory 509. The elements of thematrix Q stored in the Q memory 509 are used for calculating elements ofa next R matrix

FIG. 11 is a block diagram illustrating a multiple dimension detector(MDD) for deciding 7^(th) and 8^(th) symbols in accordance with anembodiment of the present invention.

As shown in FIG. 11, an 8^(th) symbol detector 1001 calculates distancesof each symbol for detecting an 8^(th) symbol using the matrix R of theR memory 510, the output vector R of the QR decomposer, which isinputted when the mdd_ene signal is on, and a symbol generated by asymbol generator. The operations of the 8^(th) symbol detector 1001 willbe described with reference to FIG. 11 in later.

A LLR calculator 1003 calculates a log likelihood ratio (LLR) value forthe 8^(th) symbol using the calculated distance values from the 8^(th)symbol detector 1001.

A symbol decider 1002 decides a symbol having the minimum value amongthe calculated distance values of each symbol from the 8^(th) symboldetector 1001. A R column remover and updater 1004 of the matrix Rremoves an 8^(th) column of a matrix R from the decided 8^(th) symboland updates a signal y.

A ^(7th) symbol detector 1005 calculates distances of each symbol fordetecting a ^(7th) symbol using the updated signal y through the sameoperation of detecting the ^(8th) symbol. A LLR calculator 1006calculates a LLR value for the ^(7th) symbol using the calculateddistance values from the ^(7th) symbol detector 1005.

FIG. 12 is a block diagram illustrating an 8 ^(th) symbol detector 1001shown in FIG. 11 in accordance with an embodiment of the presentinvention.

A symbol generator 1001 generates a symbol having lattice points shownin FIGS. 13 and 14. For example, 16QAM has 16 symbol lattice points.Therefore, there are 16 distances. In this case, the 7th symbol softdecision and 8^(th) symbol distance calculator 1102 performs softdecision for 16 distances. FIG. 13 shows a symbol structure when amodulation scheme is BPSK, QPSK, or 16QAM. FIG. 14 shows a symbolstructure when a modulation scheme is 64 QAM.

A 7^(th) symbol soft decision and 8^(th) symbol distance calculator 1102receives an output vector of the QR decomposer when the mdd_ene signalis on, an upper triangle matrix R of the R memory 510, and a symbolgenerated by the symbol generator 1001, performs hard decision for a7^(th) symbol to detect an 8^(th) symbol, and calculates a distancevalue of the 8^(th) symbol. The 7^(th) symbol soft decision and 8^(th)symbol distance calculator 1102 stores a received signal y which isupdated while removing an 8^(th) column of a matrix R in a y register1106.

A 6^(th) symbol soft decision and 7^(th) symbol distance calculator 1103receives the updated y value of the y register 1106, a value of the Rmemory 510, and a symbol generated by a symbol generator, performs softdecision for 6^(th) symbol, and calculates a distance value of a 7^(th)symbol. A distance accumulator and buffer 1107 accumulates distancevalues of the 8^(th) symbol and 7^(th) symbol and stores the accumulateddistance value in a register. Also, a 5^(th) symbol soft decision and6^(th) symbol distance calculator receives the updated y value of the yregister 1106, a value of a R memory, and a symbol generated by a symbolgenerator, performs soft decision for the 5^(th) symbol, and calculatesa distance of the 6^(th) symbol.

In order to detect an 8^(th) symbol, a distance value for a 5^(th)symbol, a distance value for a 4^(th) symbol, a distance value for a3^(rd) symbol, a distance value 1104 for a 2^(nd) symbol, and a distancevalue 1105 for a 1^(st) symbol are calculated through the same operationas described above.

The distance accumulator and buffer 1107 accumulates the calculateddistance values of each symbol and stores the accumulated value in aregister. The distance values stored in the distance accumulator andbuffer 1107 are transferred to the LLR calculator 1003 and the symboldecider 1002.

FIG. 15 is a diagram illustrating an interference remover 506 and ainverse matrix and weight calculator 503 in accordance with anembodiment of the present invention.

The inverse matrix calculator 1302 calculates a inverse matrix of anupper triangle matrix R using the matrix R of the R memory 510 and thevector size (1/√{square root over (norm)}) of the vector size memory511. Then, the inverse matrix calculator 1302 stores the calculatedinverse matrix in the inverse matrix memory 512.

A weight calculator 1304 calculates a weight as a square of the vectorsize (norm) of a row of the inverse matrix, calculates 1/weight using aROM table 1303, and stores the calculated values in the W memory 513.

A decided symbol generator 1301 regenerates a symbol corresponding to ademodulated data stream from the channel decoder 505. The interferenceremover 506 receives a symbol generated from the decided symbolgenerator 1301, an output value of the R memory 510, and an output valueof the Y memory 514, and removes interference from an output vector ofthe R memory and the Y memory using the regenerated symbol. If the8^(th) symbol and the 7^(th) symbol are removed, the result may beexpressed as Equation 3.

$\begin{matrix}{Y^{\prime} = {\begin{bmatrix}y_{1}^{\prime} \\y_{2}^{\prime} \\\vdots \\y_{6}^{\prime}\end{bmatrix} = {{{Rs} + n^{\prime}} = {{\begin{bmatrix}r_{1,1} & r_{1,2} & \cdots & r_{1,6} \\0 & r_{2,2} & \cdots & r_{2,6} \\0 & \vdots & \ddots & \vdots \\0 & \cdots & 0 & r_{6,6}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{6}\end{bmatrix}} + \begin{bmatrix}n_{1}^{\prime} \\n_{2}^{\prime} \\\vdots \\n_{6}^{\prime}\end{bmatrix}}}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

The WZF unit 507 performs zero forcing using an interference removedoutput vector Y′ from the interference remover 506, an inverse matrix ofthe inverse matrix memory 512, and a weight of the W memory 513. The LLRcalculator 513 calculates a log likelihood ratio (LLR) of a symbol fromthe output value of the WZF unit 507 and transfers the calculated LLR tothe decoder 508.

FIG. 16 is a flowchart illustrating a method for receiving a signal fora MIMO system in accordance with an embodiment of the present invention.

Since a MIMO receiving method according to the present embodiment wasalready described when the MIMO receiving apparatus was described above,the MIMO receiving method will be described briefly with reference toFIG. 14.

At step S1401, an unitary matrix Q, an upper triangle matrix R, and avector size are calculated through performing a QR operation on areceived signal z obtained through FFT.

At step S1402, a signal field is detected from the result of the QRoperation. Then, an inverse matrix of the matrix R is calculated usingthe vector size and the upper triangle matrix R, and a weight iscalculated using the inverse matrix of the matrix R and a ROM table. Atstep S1403, distance values for symbols are calculated through multipledimensional detection, and a LLR is calculated using the calculateddistance values. At step S1404, demodulation is performed using a LLR ofan 8^(th) symbol and a 7^(th) symbol, which is calculated throughmultiple dimensional detection. At step S1405, a symbol is generatedcorresponding to the demodulated data stream, and interference isremoved from an output vector calculated in the QR operation using thegenerated symbol. At step S1406, zero forcing is performed using aweight for the interference removed output vector and the inverse matrixof the matrix R. At step S1047, the result of zero forcing isdemodulated.

The embodiments of the present invention was described with anassumption that the number of antennas for transmitting and receiving is8 and the number of data symbols is 2. However, the present inventionmay be identically applied although the number of antennas and thenumber of data symbols are changed.

As described above, the technology of the present invention can berealized as a program. A code and a code segment forming the program canbe easily inferred from a computer programmer of the related field.Also, the realized program is stored in a computer-readable recordingmedian, i.e., information storing media, and is read and operated by thecomputer, thereby realizing the method of the present invention. Therecording median includes all types of recording media which can be readby the computer.

The present application contains subject matter related to Korean PatentApplication No. 2007-0133823, filed in the Korean Intellectual PropertyOffice on Dec. 19, 2007, the entire contents of which is incorporatedherein by reference.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A receiving apparatus of an orthogonal frequency divisionmultiplexing (OFDM) based multiple input multiple output (MIMO) system,comprising: a QR decomposing means for calculating an unitary matrix Q,an upper triangle matrix R, and a vector size for a received signal; amultiple dimension detecting means for calculating a first loglikelihood ratio (LLR) for an output of the QR decomposing means throughmultiple dimension detection; an inverse matrix and weight calculatingmeans for calculating an inverse matrix for the upper triangle matrix Rand a weight; an interference removing means for regenerating a symbolfor a demodulated data stream using the fist LLR and removinginterference from an output vector of the QR decomposing means using theregenerated symbol; and a weight zero forcing means for performing zeroforcing on the interference removed output vector from the interferenceremoving means using the inverse matrix of the upper triangle matrix Rand the weight and calculating a second LLR.
 2. The receiving apparatusof claim 1, further comprising: a signal field detection means forreceiving an output vector of the QR decomposing means and detecting asignal field from the output vector.
 3. The receiving apparatus of claim2, further comprising: a first decoding means for performingdemodulation using the first LLR outputted from the multiple dimensiondetecting means; and a second decoding means for performing demodulationusing the second LLR outputted from the weight zero forcing means. 4.The receiving apparatus of claim 3, wherein the QR decomposing meansincludes: an R calculating unit for calculating an upper triangle matrixR for the received signal; a Q update calculating unit for receiving thecalculated upper triangle matrix and the received signal and calculatingan unitary matrix Q of an update matrix; a vector size calculating unitfor calculating a vector size using the update matrix of the Q updatecalculating unit and a read only memory (ROM) table value; and a Qcalculating unit for calculating a unitary matrix Q using an output ofthe vector size calculating unit and an output of the Q updatecalculating unit.
 5. The receiving apparatus of claim 4, wherein the Rcalculating unit stores the upper triangle matrix in a first memory (Rmemory) when a QR enable signal is on, transfers the upper trianglematrix to the signal field detecting means when an enable signal forsignal field detection is on, and stores the upper triangle matrix in asecond memory (Y memory) and transfers the upper triangle matrix to themultiple dimension detecting means at the same time when an enablesignal for multiple detection is on.
 6. The receiving apparatus of claim4, wherein the vector size calculating unit calculates a vector size(norm) of a column vector from the update matrix of the Q updatecalculating unit, calculates √{square root over (norm)} and 1/√{squareroot over (norm)} using the ROM table, and stores the 1/√{square rootover (norm)} at a third memory for calculating an inverse matrix of theupper triangle matrix R.
 7. The receiving apparatus of claim 4, whereinthe Q calculating unit stores the calculated unitary matrix Q in afourth memory (Q memory) for calculating elements of a next uppertriangle matrix R.
 8. The receiving apparatus of claim 3, wherein themultiple dimension detecting means includes: a first symbol detectingunit for calculating a symbol distance value for detecting an 8^(th)symbol using an output vector of the QR decomposing means; a first loglikelihood ratio (LLR) calculating unit for calculating a LLR using thesymbol distance value outputted from the first symbol detecting unit; asymbol deciding unit for deciding a symbol having a minimum value amongthe symbol distance values of the first symbol detecting unit; a columnremoving and y updating unit for removing an 8^(th) column of the uppertriangle matrix R from the decided 8^(th) symbol from the symboldeciding unit and updating a signal y; a second symbol detecting unitfor calculating a symbol distance value for detecting a 7^(th) symbolusing the updated signal y; and a second log likelihood ratio (LLR)calculating unit for calculating a LLR using the symbol distance valuesoutputted from the second symbol detecting means.
 9. The receivingapparatus of claim 8, wherein the first symbol detecting unit includes:a symbol generator for generating a symbol having a lattice point; asymbol distance calculator for receiving the upper triangle matrix R ofthe QR decomposing means and a symbol generated by the symbol generator,performing soft decision for the symbol, and sequentially calculatingsymbol distance values; and an accumulating and buffering unit foraccumulating the calculated distance values of the symbol distancecalculator and storing the accumulated distance value.
 10. The receivingapparatus of claim 5, wherein the interference removing means includes:a decided symbol generator for regenerating a symbol using thedemodulated data stream from the first decoding means; and aninterference remover for removing the regenerated symbol from an uppertriangle matrix stored in the first memory and an upper triangle matrixstored in the second memory.
 11. The receiving apparatus of claim 3,wherein the inverse matrix and weight calculating means includes: aninverse matrix calculator for receiving a vector size and an uppertriangle matrix and calculating an inverse matrix of the upper trianglematrix; and a weight calculator for calculating a weight using an outputof the inverse matrix calculator and the ROM table.
 12. The receivingapparatus of claim 11, wherein the weight calculator calculates a weightby squaring a vector size of a row of the inverse matrix calculated bythe inverse matrix calculator, and calculates 1/weight from the ROMtable.
 13. A receiving method of an orthogonal frequency divisionmultiplexing (OFDM) based multiple input multiple output (MIMO) system,comprising: performing QR decomposing for calculating an unitary matrixQ, an upper triangle matrix R, and a vector size for a received signal;calculating a first log likelihood ratio (LLR) by performing multipledimension detection on the result of said the QR decomposing;calculating an inverse matrix for the upper triangle matrix R andcalculating a weight; regenerating a symbol for a demodulated datastream using the fist LLR and removing interference from the result ofthe QR decomposing using the regenerated symbol; and performing zeroforcing on the interference removed output vector using the inversematrix of the upper triangle matrix R and the weight and calculating asecond LLR.
 14. The receiving method of claim 13, further comprising:detecting a signal field from the result of the QR decomposing.
 15. Thereceiving method of claim 14, wherein said performing QR decomposingincludes: calculating the upper triangle matrix R for the receivedsignal; calculating an update matrix for a unitary matrix Q using thecalculated upper triangle matrix and a received signal; calculating avector size using the update matrix and a ROM table value; andcalculating an unitary matrix Q using the vector size and the updatematrix
 16. The receiving method of claim 15, wherein a vector size(norm) of a column vector is calculated from the update matrix, and√{square root over (norm)} and 1/√{square root over (norm)} arecalculated using the ROM table.
 17. The receiving method of claim 14,wherein said calculating a first LLR includes: calculating a symboldistance value for detecting an 8^(th) symbol using an output vector ofthe QR decomposing; calculating a LLR using the symbol distance valueoutputted from said calculating a symbol distance value; deciding asymbol having a minimum value among the symbol distance valuescalculated from said calculating a symbol distance value; removing an8^(th) column of the upper triangle matrix R from the decided 8 ^(th)symbol and updating a signal y; calculating a symbol distance value fordetecting a 7^(th) symbol using the updated signal y; and calculating aLLR using the symbol distance values calculated from said calculating asymbol distance value.
 18. The receiving method of claim 17, whereinsaid calculating a symbol distance value includes: generating a symbolhaving a lattice point; performing soft decision for the generatedsymbol and sequentially calculating symbol distance values using theupper triangle matrix R, and the updated signal y with an 8^(th) columnof the upper triangle matrix removed; and accumulating the calculateddistance values and storing the accumulated distance values.
 19. Thereceiving method of claim 14, wherein said calculating an inverse matrixincludes: calculating an inverse matrix of the upper triangle matrixusing a vector size and an upper triangle matrix; and calculating aweight using the inverse matrix of the upper triangle matrix and the ROMtable.
 20. The receiving method of claim 19, wherein the weight iscalculated by squaring a vector size of a row of the inverse matrix and1/weight is calculated using the ROM table.
 21. A receiving apparatus ofan orthogonal frequency division multiplexing (OFDM) based multipleinput multiple output (MIMO) system, comprising: a QR decomposing meansfor decomposing an unitary matrix Q and an upper triangle matrix R froma received signal; a multiple dimension detecting means for deciding am^(th) symbol and a (m-1)^(th) symbol through performing multipledimension detection on an output of the QR decomposing means; aninterference removing means for regenerating a symbol corresponding to ademodulated data stream using an output of the multiple dimensiondetecting means and removing interference from the output of the QRdecomposing using the regenerated symbol; and a weight zero forcingmeans for performing zero forcing on the interference removed outputvector using an inverse matrix of an upper triangle matrix R and aweight.
 22. A receiving method of an orthogonal frequency divisionmultiplexing (OFDM) based multiple input multiple output (MIMO) system,comprising: decomposing an unitary matrix Q and an upper triangle matrixR from a received signal; deciding an m^(th) symbol and a (m-1)^(th)symbol through performing multiple dimension detection on an output ofsaid decomposing; regenerating a symbol corresponding to a demodulateddata stream using the output of said deciding and removing interferencefrom the output of said QR decomposing using the regenerated symbol; andperforming zero forcing on the interference removed output vector usingan inverse matrix of an upper triangle matrix R and a weight.